184 MANTON COPELAND 
the current without food and 1636 centimeters with the food 
present. The distances moved across the current are not recorded. 
A snail failed in but one case to increase its arrivals upstream 
when the fish were there (Animal number four). It should be 
noted, however, that this individual showed a greater tendency 
to move against the current when food was present than it did 
in its absence. The force of the current infrequently caused a 
snail to lose its foothold and slip a short distance on the glass, 
but it soon recovered itself and continued its locomotion. The 
total distance moved as a result of slipping in the forty trials 
was but little over fifty centimeters, over forty of which were 
recorded for this same animal in its trials with food juices in the 
water. 
The average time taken by the snails in reaching the seventy- 
five centimeter line up the current without food, in six trials, was 
approximately twenty-seven minutes, and with food present, in 
sixteen trials, twenty-nine minutes. 
The experiment indicates that snails which are inconstant in 
their reactions to a current, or more often go downstream, move 
more frequently against a current when it carries dilute food 
juices; in truth, they exhibit olfactory responses leading to the 
discovery of distant food. When the animals tested were al- 
lowed to continue their progress against the current beyond the 
seventy-five centimeter line, they usually arrived at the fish 
and began feeding. 
2. Organs sensitive to food extracts 
Having made certain that Alectrion responds actively to 
dilute food stimuli, experiments were begun to determine the 
sensitiveness of the external parts of the snail to odorous material, 
in the hope of discovering the olfactory receptor. 
An extract of fish meat was prepared by grinding muscle tissue 
of Fundulus in sea water and filtering the product. A small 
amount of dry carmine was added to the filtrate, in order to 
make it visible in water. 
The tentacles. The tentacles were first tested. When the 
fish extract was squirted over the tentacle of a moving snail by 
